The invention relates to a finely divided crystalline layered sodium disilicate of the formula NaMSixO2x+1.yH2O, where M is sodium or hydrogen, x is a number from 1.9 to 4, and y is a number from 0 to 20, to a process for its preparation and to its use.
Crystalline layered sodium silicates (phyllosilicates), in particular those of the formula NaMSixO2x+1.yH2O, where M is sodium or hydrogen, x is a number from 1.9 to 4, and y is a number from 0 to 20, and preferred values for x are 2, 3 or 4, have proven to be suitable replacements for the builders phosphate and zeolite, especially in detergents and cleaners.
The use of the abovementioned crystalline phyllosilicates for softening water is described, for example, in EP-A-0 164 514. Preferred crystalline phyllosilicates are those in which M is sodium and x assumes the values 2 or 3.
Preferred replacements are either beta- or delta-sodium disilicates (Na2Si2O5.yH2O), it being possible to obtain beta-sodium disilicate, for example, by the process in PCT/WO 91/08171.
A commercially available crystalline sodium disilicate which corresponds to the abovementioned formula is, for example, SKS-6 from Clariant GmbH. This product is composed of the various polymorphous phases of sodium disilicate and thus consists of alpha-disodium disilicate, beta-disodium disilicate and delta-disodium disilicate. Preference is given to as high as possible a content of delta-disodium disilicate. The commercial product may also comprise components of noncrystallized sodium silicate.
The aim has hitherto always been to prepare sodium disilicates which comprise as high a content as possible of only one polymorphous phase, such as, for example with a delta-disodium silicate content of more than 90% by weight or above.
The sodium disilicates known hitherto can already satisfy a large number of the requirements placed on them. For example, they generally have high calcium-binding capacity and their other washing and performance properties are sufficient for many areas.
However, there continues to be a requirement for suitable substances which have very high calcium-binding capacity and at the same time produce only small dissolution residues in water (referred to below as sieve residue).
This object is achieved by a finely divided crystalline layered sodium disilicate of the type mentioned at the outset, which comprises
from 0 to 40% by weight of alpha-disodium disilicate
from 0 to 40% by weight of beta-disodium disilicate
from 40 to 100% by weight of delta-disodium disilicate
from 0 to 40% by weight of amorphous components.
The abovementioned alpha-disodium disilicate corresponds to the Na SKS-5 described in EP 0 164 514 B1, characterized by the X-ray diffraction data reproduced therein, which are assigned to the alpha-Na2Si2O5, whose X-ray diffraction patterns are registered with the Joint Committee of Powder Diffraction Standards under the numbers 18-1241, 22-1397, 22-1397A, 19-1233, 19-1234, 19-1237.
The abovementioned beta-disodium disilicate corresponds to the Na SKS-7 described in EP 0 164 514 B1, characterized by the X-ray diffraction data reproduced therein which are attributed to the beta-Na2Si2O5, whose X-ray diffraction patterns are registered with the Joint Committee of Powder Diffraction Standards under the numbers 24-1123, 29-1261.
The abovementioned delta-disodium disilicate corresponds to the Na SKS-6 described in EP 0 164 514 B1, characterized by the X-ray diffraction data reproduced therein which are attributed to the beta-Na2Si2O5, whose X-ray diffraction patterns are registered with the Joint Committee of Powder Diffraction Standards under the number 22-1396.
The finely divided crystalline layered sodium disilicate according to the present invention is notable for a binding capacity for water hardeners (calcium-binding capacity) which is greater compared with the prior art, and also for the fact that the dissolution residues in water (defined below by the sieve residue) are considerably reduced.
Preferably, the finely divided crystalline layered sodium disilicate comprises
from 0 to 20% by weight of alpha-disodium disilicate
from 0 to 30% by weight of beta-disodium disilicate
from 50 to 95% by weight of delta-disodium disilicate
from 0 to 20% by weight of amorphous components.
Particularly preferably, the finely divided crystalline layered sodium disilicate comprises
from 0 to 10% by weight of alpha-disodium disilicate
from 0 to 15% by weight of beta-disodium disilicate
from 70 to 90% by weight of delta-disodium disilicate
from 0 to 10% by weight of amorphous components.
The finely divided crystalline layered sodium disilicate is preferably free from sodium metasilicate or NS phases. It is also free from so-called NS phases, as defined, for example, in PCT/WO 97/19156 and in JP 7/327995 A1 and to which reference is here expressly made.
Preferably, the finely divided crystalline layered sodium disilicate has a d90 value of  less than 100 xcexcm.
Preferably, the finely divided crystalline layered sodium disilicate has a d90 value of  less than 60 xcexcm.
Preferably, the finely divided crystalline layered sodium disilicate has a calcium-binding capacity of more than 170 mg of CaCO3/g at 30xc2x0 C. and 17xc2x0 German hardness.
Particularly preferably, the finely divided crystalline layered sodium disilicate has a calcium-binding capacity of more than 180 mg of CaCO3/g at 30xc2x0 C. and 17xc2x0 German hardness.
In particular, the finely divided crystalline layered sodium disilicate has a calcium-binding capacity of more than 190 mg of CaCO3/g at 30xc2x0 C. and 17xc2x0 German hardness.
Preferably, the finely divided crystalline layered sodium disilicate has a sieve residue of less than 60%.
Preferably, the finely divided crystalline layered sodium disilicate has a sieve residue of less than 40%.
Preferably, the finely divided crystalline layered sodium disilicate has a sieve residue of less than 30%.
The invention also relates to a process for the preparation of finely divided crystalline layered sodium disilicates, which comprises grinding a sodium phyllosilicate having a particle diameter d50 of from 80 to 400 xcexcm to a d90 value of  less than 100 xcexcm.
Preferably, the finely divided crystalline layered sodium disilicate is ground to a d90 value of  less than 60 xcexcm in the above process.
Preferably, the process is carried out using a vibrating mill, ball mill, roller mill, pendulum roller mill or air-jet mill.
The invention also relates to the use of the finely divided crystalline layered sodium disilicates according to the invention for the preparation of detergents and cleaners, including dishwashing detergents.
The invention likewise relates to the use of the finely divided crystalline layered sodium disilicates according to the invention as builders.
The invention likewise relates to detergents and cleaners which comprise a finely divided crystalline layered sodium disilicate according to the invention, in particular in addition to other ingredients, active ingredients and auxiliaries. The amounts given below are, despite it not always being expressly mentioned, made up to a total of 100% by weight by customary ingredients, active ingredients and auxiliaries for detergents and cleaners.
Preferably, such detergents and cleaners comprise from 1 to 80% by weight of the finely divided crystalline layered sodium disilicate according to the invention.
Preferably, such detergents and cleaners comprise from 1 to 80% by weight of zeolite and from 1 to 80% by weight of the finely divided crystalline layered sodium disilicate according to the invention.
Preferably, such detergents and cleaners comprise from 1 to 80% by weight of zeolite, from 1 to 80% by weight of crystalline sodium phyllosilicate and from 1 to 80% by weight of the finely divided crystalline layered sodium disilicate according to the invention.
Preferably, such detergents and cleaners comprise from 1 to 80% by weight of the finely divided crystalline layered sodium disilicate according to the invention and from 1 to 10% by weight of citric acid or salts of citric acid.
Preferably, such detergents and cleaners comprise from 1 to 80% by weight of zeolite, from 1 to 80% by weight of the finely divided crystalline layered sodium disilicate according to the invention and from 1 to 10% by weight of citric acid or salts of citric acid.
Preferably, such detergents and cleaners comprise from 1 to 80% by weight of the finely divided crystalline layered sodium disilicate according to the invention and from 0.5 to 5% by weight of modified cellulose.
Preferably, such detergents and cleaners comprise from 1 to 80% by weight of zeolite, from 1 to 80% by weight of the finely divided crystalline layered sodium disilicate according to the invention and from 0.5 to 5% by weight of modified cellulose.
Preferably, such detergents and cleaners comprise from 1 to 80% by weight of zeolite, from 1 to 80% by weight of crystalline sodium phyllosilicate, from 1 to 80% by weight of the finely divided crystalline layered sodium disilicate according to the invention and from 0.5 to 5% by weight of modified cellulose.
The abovementioned cellulose can, where appropriate, be chemically and/or mechanically modified.
Surprisingly, it has been found that the finely divided crystalline sodium disilicate according to the invention also has increased calcium-binding capacity.
The crystalline sodium disilicate according to the invention also produces considerably fewer residues compared with commercial crystalline sodium disilicates, which can be demonstrated using the sieve residue test. The meshes of the metal screening gauze used, with a mesh size of 20 xcexcm, simulate the meshes of textile fabric. Instead of metal screening gauze it is also possible to use a polyester screening fabric having the same mesh size. In the sieve residue test, the finely divided crystalline layered sodium disilicates according to the invention have d90 values below 60 xcexcm, indicating considerably reduced sieve residues.
The finely divided crystalline sodium disilicate according to the invention can be used advantageously as a builder. It can be used over the whole spectrum of detergents which are customary nowadays, such as compact heavy-duty detergents, compact color detergents, heavy-duty detergents of lower bulk density etc.
Detergents which comprise the finely divided crystalline sodium disilicate according to the invention produce significantly fewer inorganic encrustations in model washing tests, which can be demonstrated by determining the ash. The latter remains when the fabric is incinerated.
Inorganic encrustations consist on the one hand from water hardness precipitated in the form of calcium carbonate and also of residues of detergent builders which have not completely dissolved or have settled out again. They reduce the wearing comfort of the laundry item by making it scratchy and reduce the durability. The use of the finely divided crystalline sodium disilicate in detergents thus produces a significant advantage in terms of longevity of the fabric and comfort when wearing.
The properties of the finely divided crystalline layered sodium disilicate according to the invention were determined using the following methods of measurement.
Determination of the Calcium-binding Capacity
A mixture of a buffer stock solution and deionized water is introduced into an ErWeKa dissolution tester, stirred and heated to 30xc2x0 C. The buffer stock solution is an aqueous solution of glycine, sodium chloride, calcium chloride and sodium hydroxide in suitable concentrations. The calcium-sensitive electrode (model 932001 from Orion) is dipped into the solution and calibrated by replenishing the solution with a calcium stock solution. This is carried out using the evaluation unit EA 940 from Orion. After replenishing, the solution has a water hardness of 17 degrees German water hardness (17xc2x0 German hardness). At the same time as the substance under investigation (1 g) is added, the Orion EA 940 is started. The pH of the measurement solution is 10.2. The Orion EA 940 gives the concentration of free calcium ions at specific time intervals. Using the known initial weight of calcium, the concentration of free, nonbonded calcium ions after 10 min is used to deduce the amount of bonded calcium, the calcium-binding capacity. This is given in mg of CaCO3/g.
Determination of the Particle Size Distribution Using a Microtrac Granulometer
The particle size in an aqueous dispersion is determined using a Microtrac ASVR/FRA granulometer from Leeds and Northrup. The parameter measured is the reflection or diffraction of a laser beam on penetrating the dispersion. For this, 400 ml of ethanol are pumped through the laser measuring cell. The sample of solid (e.g. 70 mg) is metered in automatically, and the particle size distribution is determined after 10 min. The evaluation unit of the device calculates the d50 and the d90 value.
Determination of the Particle Size Distribution by Sieve Analysis
In a sieve machine from Retsch, the inserts with the desired sieves are used. The mesh size of the sieve decreases from top to bottom. 50 g of the powder to be investigated are placed onto the widest sieve. By vibrating the sieve machine, the powder material is conveyed through the various sieves. The residues on the sieves are weighed and related mathematically to the initial weight of material. The values can be used to calculate the d50 and d90 value.
Sieve Residue Test
For this, 800 ml of tap water [water hardness 14xc2x0 German hardness] are heated to 20xc2x0 C. and stirred using a propeller (straight-arm) stirrer. 2 g of the test substance are added and stirred for 20 minutes. Using the slight vacuum of a water-jet pump, the dispersion is sucked through a 20 xcexcm metal sieve gauze. The sieve is dried at 80 to 100xc2x0 C. for one hour in a circulating drying cabinet. The increase in weight is related to the initial weight and standardized to 100% and referred to as residue.
Preparation of the Test Detergent (Table 2)
The optical brighteners are stirred into a quarter of the nonionic amount and mixed with half of the amount of soda in a household multimixer (Braun). Using a Lxc3x6dige plough share mixer, the remainder of the soda and all of the zeolite and Polymer are mixed for 15 minutes at 300 rpm. Half of the remaining amount of nonionics is then sprayed on in 5 minutes. The SKS-6 or the ground product is then added and mixed for 10 minutes. The remaining second half of nonionics is then sprayed on in a further 5 minutes. Finally, anionic, soap, antifoam, phosphonate and optical brighteners are added and then mixed for 10 minutes at 300 rpm. In a wobble mixer, the mixture from the Lxc3x6dige mixer is admixed with perborate, TAED and enzymes with low shear stress and mixed for 15 minutes.
It is, of course, also possible to change the order in which the substances are added.
Washing Tests
In a standard domestic washing machine (model: Novotronic 927 WPS, Miele) specific test fabrics are washed repeatedly (15 times) at 60xc2x0 C. and a water hardness of 18xc2x0 German hardeners using the test detergent in an amount of 65 g of test detergent/wash cycle. The test fabrics, which are, in particular, a cotton terry fabric (Vossen), in each case a cotton double-rib fabric, polyester/cotton blend (type 20A) and standard cotton fabric (type 10A) from Wxc3xa4schereiforschung Krefeld Testgewebe GmbH and a standard cotton fabric from the Swiss Materials Testing Institute, St. Gallen, Switzerland, are supplemented with further laundry ballast (3.75 kg). After 15 washes, a sample is taken from each of the fabrics and ashed in a muffle oven at a temperature of 1000xc2x0 C. for a period of 24 hours.